1. Field of the Invention
This invention relates to circuit breakers having a contact arm spring subassembly for providing pressure to maintain the contacts closed, and to a method and apparatus for making the subassembly to simplify the assembly of the circuit breaker.
2. Background Information
Molded case circuit breakers have a moveable contact mounted on a contact arm which is pivoted by a carrier between a closed position in which the moveable contact contacts a fixed contact to connect a protected circuit to a source and an open position in which current to the load is interrupted. Typically, the contact arm is made up of a stack of copper laminations supported in the carrier to operate as a single conductor. Contact springs are provided in the carrier to apply contact pressure to the contacts when they are closed and to allow for contact wear. Typically in molded case circuit breakers, arcing contacts are provided in addition to the main contacts. The springs for the contact arm laminations carrying the arcing contacts are selected such that the arcing contacts do not separate until after the main contacts open. With this arrangement, the arcing contacts take the major wear associated with interrupting the arcs which are struck when interrupting large currents.
In some molded case circuit breakers, the contact springs are supported in a contact spring clip. This contact spring clip is an elongated channel member having a series of cone shaped protrusions punched into the bottom wall which serve to locate the individual helical compression springs for alignment with the respective contact arm laminations. The contact arm laminations, the carrier, and the contact spring clip and individual springs are assembled along with flexible shunts, shunt plates, and barriers between the laminations to form a moving conductor assembly. Currently, it is difficult to maintain the proper position of all of the parts, and especially the springs, while making the assembly. While the cone shaped protrusions in the spring clip provide a point of reference for the springs, they are not visible throughout assembly. As a result, the springs could be misaligned, or possibly drop out without notice. These assembly problems directly affect product cost due to additional assembly time needed to assure proper spring retention and alignment. Rework resulting from mislocated and missing springs and disassembly of misassembled product is significant. Multi-phase circuit breakers require separate moving conductor assemblies for each phase, which compounds the problem.
There is a need, therefore, for an improved circuit breaker which can be assembled easily and reliably.
There is a concurrent need for an improved method and apparatus for assembling multi-phase circuit breakers having multiple contact springs for each moving conductor assembly.
There is a related need for an improved subassembly of contact springs and an associated spring clip to facilitate assembly of the circuit breaker.
There is also a need for such a method and apparatus which are flexible enough to easily accommodate assembly of circuit breakers having different numbers of contact springs.